1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel that is adapted for increasing the viewing angle and picture quality in a diagonal direction, and a fabricating method thereof.
2. Discussion of the Related Art
A liquid crystal display modulates light that is incident to a liquid crystal cell by controlling an electric field applied to the liquid crystal cell, thereby displaying a picture. The liquid crystal display (LCD) device is generally classified into a vertical electric field type LCD and a horizontal electric field type LCD in accordance with the direction of the electric field that drive the liquid crystal.
The vertical electric field type LCD has a pixel electrode and a common electrode that are vertically positioned opposite to each other formed in an upper substrate and a lower substrate, respectively. The opposing electrodes apply an electric field to a liquid crystal cell in a vertical direction by a voltage applied to the electrodes. A twisted nematic (TN) mode is typical of the vertical electric field type LCD and is currently most widely used. Although, the twisted nematic mode has a relatively high aperture ratio, the refractive index of the liquid crystal changes dramatically depending on the viewing angle of the user. Therefore, it is difficult to obtain a wide viewing angle using a vertical electric field type LCD.
An in-plane switching (IPS) mode typical of horizontal electric field type LCDs applies an electric field between electrodes that are formed on the same substrate to drive the liquid crystal molecules. In the IPS mode, as shown in FIG. 1A, there are pixel electrodes 16 and common electrodes 15 formed on a lower glass substrate 18. An electric field 20 is formed in the horizontal direction by a voltage difference applied between the electrodes 15, 16. The liquid crystal molecules 14 are forced to rotate within the surface direction of the substrate by the horizontal electric field 20 to modulate the polarizing component of the light passing through the liquid crystal layer.
In FIG. 1B, polarizers 11 and 19 are formed on the upper glass substrate 12 and the lower glass substrate 18. When looking from the front (i.e., front observation), polarized light absorption axes, or transmission axes 11A,19A in the polarizers 11,19 are perpendicular to each other. The alignment films 13 and 17 are formed on the upper glass substrate 12 and the lower glass substrate 18, respectively. Generally, the alignment films are formed of polyimide and treated to be aligned by rubbing, for example.
In the IPS mode, light transmitted through the liquid crystal layer passes through the upper polarizer 11 if the linear polarized light is changed by the liquid crystal layer. If the polarizing component of the light that passes through the liquid crystal layer is not changed, then the light does not pass through the upper polarizer 11.
In the IPS mode, the electric field generated between pixel electrode 16 and common electrode 15 to be applied to the liquid crystal molecules 14 is bent such that the light switching is not normal to the electrodes 15 and 16. The result is a low aperture ratio in the IPS mode. Further, when an IPS mode LCD device is viewed in a diagonal direction, as shown in FIG. 2 (i.e., oblique observation), the angle of the polarized light absorption axis 11A of the upper polarizer 11 and the polarized light absorption axis 19A of the lower polarizer 19 appears to be greater than 90°. As a result, light leaks out from a black screen because light is not fully polarized. Consequently, contrast is reduced in the diagonal direction. Deterioration of contrast in the diagonal direction can be seen in FIG. 3, which shows an experimental result of the viewing angle characteristics of the in-plane switching mode. As shown in FIG. 3, there is almost no light leakage during front observation, i.e., when the observer is at right angles with the screen (blue). However, light leakage occurs in the diagonal direction when the angle between the polarized light absorption axes 11A and 19A is greater than 90° (baby blue, green, yellow, red).